Idea for any budding entrepreneur

So Google wallet. What is the obvious flaw to the system that moves payment away from an inert plastic object to a battery based consumer device?  What happens when the power source goes is probably a good one.

Now there are lots of mobile phone chargers out there that work off a batteries, but who has the dominance at till/ point of purchase points- just ready for that impulse/  last minute purchase [assuming you have power to make one!]

So who is going to put those chargers at the tills?